Concentration of iron ores



June 21,1955 L. A. RcsE 2,711,248

CONCENTRATION OF IRON ORES Filed June 1, 1951 2 Sheets-Sheet l Ihwentor ZAWBZNCE A. i205 (Ittomeg June 21,1955 A GE 2,711,248

CONCENTRATION OF IRON ORES Filed June 1, 1951 2 Sheets-Sheet 2 CONVENTIONAL WET-MAGNET! SEPARATION MAqucnc ORE NON-MAQNETIC OR n i MAGNETIC REFLux TWA$TE CONCENTRATOR STAGEI UNDERFLOW- I OVERFLOW-I To WASTE MAquEncREFLuw COMCENTRATOR STAqEII UuoERFLow-H OVERFLQW-JI I 1 v MAqNETmRaFLux TOWAETE CONCENTR'ATOR su em UNOERFLOW-m OvERFLoW-III 3m entor LAWRENCEA. [P05 United States Patent Oflice 2,111,248 CONCENTRATION OF IRON ORES Application June 1, 1951, Serlal No. 229,345 6 Claims. (Cl. 209-39) This invention relates to a process for concentrating magnetic iron ores and is more particularly concerned with the concentration of low grade magnetic iron ores.

The low grade iron ores to which this invention is primarily directed are siliceous magnetites in which the predominantly silica gangue is intimately associated with the magnetite particles. Such ores may contain iron in amounts from 26% up to perhaps 36% and silica in amounts ranging up to 43% or 44%. The'iron is predominantly in the form of magnetite, the proportion of this form reaching 88% or 89%; the balance is principally hematite. Such ore may be concentrated to some degree by conventional wet or dry magnetic processes. However, it is quite generally impracticable and in many cases impossible by conventional processes to recover an economic proportion of the iron and reduce the silica content of the concentrate to a tolerable figure. The difliculty appears to hem the intimate association of silica particles with magnetite particles. Magnetic'separation or concentration processes be first ground to a particle size engage or unlock the particles of silica from those of magnetite. The ores with which my process is concerned are characterized by such intimate association or magnetite and sidica that even when they are ground to exceeding fineness, such as minus 400 mesh for example, a very appreciable amount of silica is still locked or intimately engaged with these fine magnetite particles. The cost of such fine grinding is a very significant factor in the treatment of these ores and militates against their use. Furthermore, even when such ores are finely ground the product of conventional magnetic separation processes is not too desirable because the highest iron content is always associated with the very finest grains and the coarser screen fractions are invariably higher in silica and other gangue materials.

small enough to dis- If such ores are to be commercially useful, the mid dlings which contain most of the silica, although they may represent a relatively small portion of the weight of the ore, must be separated from the finer particles which contain the bulk of the iron. Such a separation is impossible with conventional magnetic separators however because of their non-selective action on mixed particles of magnetite and gangue. These separators attract particles containing magnetite and 80% gangue for example, almost as readily as those containing 80% magnetite and 20% gangue and consequently cannot separate out and divert the middling particles previously mentioned.

It is an object, therefore, of my invention to provide a process for concentrating low grade ores of the char-' acter described which makes possible'th'e segregation and diversion of middling particles high in gangue content. a process for magnetic concentration of such ores'which does not require the extremely fine grinding hitherto considered necessary. Other objects of my invention will appear in the course of the following description.

require that the ore It is another object of my invention to provide' 7 2,711,248 Patented- June, 2 1, 1955 My process may be characterized as a combination of magnetic separation and hydraulic classification. The process of magnetizing ifinely divided ore before intro-v ducing it into a hydraulic classifier is known and it is not to be confused with my process which comprehends hydraulic classification of finely divided particles in. a magnetic field. I denominate my process the magnetic reflux concentration of orefland refer .to the apparatus employed therein as a magnetic reflux concentrator.

In the accompanying drawings, which illustrate a present preferred embodiment of my invention,

Figure 1 is a diagrammatic elevation of a magneticv reflux concentrator an r Figure 2 is a flow sheetillustrating the procedures comprehended by my process... I

My invention will be most readily understood by sequence of reference to Figure which illustrates a two-stage mag-- netic reflux concentrator. Additional stages may be required in a commercial embodiment of my process but their operation will become obvious from the explanation of the two shown. The first stage of this con-.. centrator is designated generally as 1 and the second as 2. The'first stage comprises an upright vessel or chamber 4 of non-magnetic material, provided with an-ore; pulp inlet 5, a waterfinlet 6, an overfiow 7 and an underflow pipe 8. The underflowlpipe is closed. by a valve 9 which may be operated from outside the vessel by means not here .shown. A perforated plate 10.is positioned crosswiseof the vessel at a point above the. water inlet 6, and a magnet 11 surrounds the vessel above the ore pulp inlet 5. This magnet is outside the walls of vessel 4. The second stage or my apparatus is likewise provided with an upright vessel 12 having an ore pulp inlet 13 which-communicates with'the underflow pipe 8'of the preceding stage, a water inlet 14, an overflow 15, and an underflow pipe 16 provided with a valve 17. A perforated plate 18 corresponds to the similar plate 10 in the first stage 1 and a magnet 19 surrounds the vessel 12 at a region above the pulp inlet 13. The upright chamber 4 with perforated plate 10 and water inlet 6 therebelow comprise the essential'features of a hindered settling hydraulic classifier, the con-f ventional operation of which is well known. In my process iron ore which has been first comminuted andthen passed through a conventional wet magnetic separator to remove the free gangue is introduced as an ore pulp through the inlet 5 of the apparatus illustrated. Water under pressure is constantly entering the chamber 4 through the inlet pipe 6, rising through the perforated plate to the top of the chamber and overflowing through the outlet 7. These upwardly flowing currents of water carry the ore pulp upwardly into the region of chamber 4 surrounded by the magnet 11. This magnet, which may be a permanent magnet or an electromagnet ener gized from a direct current source, not shown, main tains a magnetic field in this portion of the chamber. This magnetic field magnetizes the particles ofmagnetite contained in the water-borne ore but, of course, does not magnetize the gangue-particles. Magnetizedore par-' ticles free. from gangue are attracted to one another" and form rather loosely compacted masses which, because of their weight, tend to sink out of the magneticfield andtoward the bottom of the chamber. Particles of ore intimately.associated, with relatively small amounts of gangue are also attracted in some degree but with a reduced force. This I believe is because the presence of the gangue prevents the magentite'particles closelyf' approaching each other and it is of course known that the-force of attraction between magnetizedbodies is inversely proportional ,to, thesquare of the distance bee tween them. Magnetite particles associated with substantial proportions of gangue are not attracted together 7 I masses and separate these articles bound by lesser at:

tractive forces, that is, the particles containing gangue. These particles when detached from thelarjger masses are borne upward by the water streams and'into the magnetic field where the cycle maybe repeated. This reflux is allowed to continue until substantially all particles associated with less than .a predetermined amount'of gangue sink into the underflow and substantially all those associated with greater amounts are washed out into the overflow. The redetermined separation point depends upon the strength of the magnetic field, which may be adjusted by known'ways, sneh'asb'y adiusting the current supplied to the electromagnet, and the force of the upwardlyflowing water, which is easily controlled .by a valve. The'under'flow' from the first stage of my process may then be conducted into 'a' second stage which is identical with the first except that the magnetic field and water pressure may be adjusted to different values so that a second traction of particles associated with gangue is separated and washed out into the overflow. The product or this second stage may, of course, be introduced into additional stages and any desired number of middling fractions separated out. The final product is recovered frornthe underfiow of the last reflux classifier stage. The overflow products of the various stages may be discarded, or recycled as desired. If recycled, the overflow products must pass through a c'omminution stage to liberate additional iron mineral from the gangue. prefer to carry out my rocess in such a way that the overflow from the first stage is higher in gangue than the overflow from the secnd stage which is higher in gangue than the overflow from the third stage, if any, and so on. j

The ilow sheet in Figure 2 ndicates graphically the sequence of steps of a process utilizing three stages of magnetic reflux concentration as described above.

I have applied the process of my invention successfully to two Michigan iron ores which are not amenable to treatment by conventional concentration processes. These ores, as taken from the mine, exhibit the analyses listed below:

F V v 810 Fepresent e. pera, peras m cent cent netlte,

percent A. 26.07 34.18 as 5 B 35.82 i 43.22 86: 4

A batch of ore Awas ground so that all of it passed through a 100 mesh sieve. It was then processed as-indicated by the How sheet of Figure 2 through a conventional wet magnetic separator and then through a three-stage magnetic reflux concentrator embodying the process of my invention. The composition of the ore entering and leaving the magnetic reflux concentrator and the compositions of the overflow from the three stages are tabulated below:

. are tabulated below It will be observed that the overflow from the first stage of my'process contained slightly over 'SiOz" whicjll' comprised 17.5% of the total amount of SiOz of the ore treated. Similarly, the overflow from the second stage analyzed almost 36% SiOz which comprised 6.7% of the total SiOz introduced. The iron loss in each of these overflows amounted however only to 1.3% of that originally introduced. The final underflow product contained 93.6% of the iron originally present and 66.7% of the silica. 'Tlhisis quite a high recovery of iron and was 7 made possible because the original silica content of the ore was not excessively high.

A batch of ore B, was likewise ground sopthat all oi it passed through a 100 mesh sieve and was then concentrated by the process illustrated inthe flow sheet of Figure 2. This ore after passing through the wet magnetic separator was considerably higher in silica than ore A. The analyses of this material at Table II.

'Pzlr fgnzi'Dis- Percent lorcent Percent J u on Ewan w re s10,

Fe SiOt Magnetic Se arator Output" 100.0 54. 22.86 100.0 100.0 Cone. Over ow 1 6.5 20.13 62.00 2.4 19.9 Gone. Overflow #2 5. l 29.61 51 38 2. 8 13. 0 Cone. Overflowi ilfl 7. 5, 43 1 33.04 5.9 "12.2 Undernow "l 80. 9 13. 74 S8. 9 54. 9

It will be observed that my process has recovered.,8 8.9% of the iron in the ore introducedinto the magneticrcflux concentrator and has gotten rid of 45.1% of the silica,

This is a very satisfactory performance with an ore ground only to minus 100 mesh. If theore is qgroundto to minusZOO mesh but otherwiseprocessed as ,abovegavc;

; the following results:

. Table in Percent Dis rmfluct IeieentIeleent Pergnt "l i Fe [slot Magnetlcsearatoroutpnh. lO0.01 ;67. 08- 710.23 100.0 5100.0 Cone. Over ow #1- 5.9 24.86 55.73 2.5 20.3 Conciherflow-fi. as 37.24 40.112 4.4 10:8 Gone. Overflow #3. 3.0 51.02 24.40 4.3 7.4 Underflo\v-. 82.fl 62.48 10. 04 88.3, 55.5

7, Here again my process brought about a removal of 44.5% of the silica with a recovery"of'88,.8% of .the iron;- The results of Tables Hand 111 showthat my process. does notdependupon costly. fine grinding oflhe ore for;

its effectiveness.

Although I have described and illustrated a present preferred embodiment of :my invention it isqnot to be considered as limited thereto. only by the; appended claims.

I claim: I

1. The process of treating iron ore. composed of hetero.

geneous fineparticles of magnetizable iron mineral associated with'gangue comprising carrying the ore particles upwardlyin a-stream of water into amagneticfield, magnetizing the iron mineral particles, thereby causing them to: form by :mag'netic. attraction loosely compacted 1 masses associated'withganguewhichsink out of the magnetizing. field, disintegrating .thcsejloosely compacted masses :by the stream of watentherebyrdissociating.gangueparticlesr from. i191! mineralpa'rticles; washing-dissociated gang'ue' 7 various stages of my process My; invention is limited i 2. The process of claim 1 in which the strength of the magnetic field and the stream of water are adjusted to disintegrate the loosely compacted masses associated with gangue in excess of a prescribed amount, and iron mineral particles associated with gangue below this prescribed amount are collected in the underflow.

3. The process of claim 1 in which the stream of water is adjusted to disintegrate loosely compacted masses as sociated with gangue when said masses have sunk out of the magnetic field, but not to disintegrate said masses in the magnetic field.

4. The process of treating iron ore composed of heterogeneous fine particles of magnetizable iron mineral associated with gangue comprising carrying the ore parti cles upwardly in a stream of water into a magnetic field extending radially about the axis of the stream, magnetizing the iron mineral particles, thereby causing them to form by magnetic attraction loosely compacted free masses associated with gangue which sink out of the magnetizing field, disintegrating these loosely compacted masses by the stream of water, thereby dissociating gangue particles from iron mineral particles, washing dissociated gangue particles out in the overflow and collect ing iron mineral particles in the underflow.

5. The process of treating iron ore composed of heterogeneous fine particles of magnetizable iron mineral associated with gangue comprising carrying the ore particles upwardly in a stream of water into a magnetic field, magnetizing the iron mineral particles, thereby causing them to form by magnetic attraction loosely compacted masses associated with gangue which sink out of the magnetizing field, disintegrating these loosely compacted masses by the stream of water, thereby dissociating gangue particles from iron mineral particles, carrying the dissociated iron mineral particles upwardly again into the magnetic field, washing dissociated gangue particles out in the overflow and collecting iron mineral particles in the underflow.

6. The process of treating iron ore composed of heterogeneous fine particles of magnetizable iron mineral associated with gangue in a range of intimacies comprising carrying the ore particles upwardly in a stream of water into a magnetic field, magnetizing the iron mineral particles, thereby causing them to form by magnetic attraction loosely compacted masses associated with gangue which sink out of the magnetic field, disintegrating the loosely compactedmasses by the stream of water, thereby dissociating from the iron mineral particles gangue particles less intimately associated therewith, carrying the iron mineral particles still associated with gangue upwardly again into the magnetic field, washing dissociated gangue particles out in the overflow and collecting iron mineral particles in the underflow.

References Cited in the file of this patent UNITED STATES PATENTS 509,728 Gillespie Nov. 28, 1893 827,499 Bring -2 July 31, 1906 954,015 Bent Apr. 5, 1910 7 954,016 Bent Apr. 5, 1910 1,392,413 Gow Oct. 4, 1921 1,491,600 Fernow Apr. 22, 1924 2,078,513 Stearns Apr. 27, 1937 2,258,194 Queneau Oct. 7, 1941 2,276,075 Wuensch Mar. 10, 1942 2,309,923 Robertson Feb. 2, 1943 2,468,586 Braund Apr. 26, 1949 2,558,635 Vedensky June 26, 1951 2,563,086 Verschoor Aug. 7, 1951 2,612,262 Symington et a1 Sept. 30, 1952 FOREIGN PATENTS 226,588 Great Britain Dec. 17, 1924 416,534 Great Britain Sept. 17, 1934 681,907 Germany Oct. 4, 1939 

1. THE PROCESS OF TREATING IRON ORE COMPOSED OF HETEROGENEOUS FINE PARTICLES OF MAGNETIZABLE IRON MINERAL ASSOCIATED WITH GANGUE COMPRISING CARRYING THE ORE PARTICLES UPWARDLY IN A STREAM OF WATER INTO A MAGNETIC FIELD, MAGNETIZING THE IRON MINERAL PARTICLES, THEREBY CAUSING THEM TO FORM BY MAGNETIC ATTRACTION LOOSELY COMPACTED MASSES ASSOCIATED WITH GANGUE WHICH SINK OUT OF THE MAGNETIZING FIELD, DISINTEGRATING THESE LOOSELY COMPACTED MASSES BY 